This invention relates to a method for forming a deposit of a first metal on a second metal by friction surfacing.
British Patent Specification No. 572789 (Klopstock) describes a method for joining or welding metals in which a rotating rod or bar of welded metal is fed into contact with the metal part or parts to be treated with such continuity of pressure and is moved relatively thereto at such speed that the frictional heat generated causes the end of the rod or bar and the metal to attain welding temperature. The result is that the metal of the rod or bar becomes deposited on the metal under treatment to form a local enlargement to join two juxtaposed metal parts together or fills in blow-holes or the like in the surface under treatment.
In the Klopstock method, portions of the workpiece encountering the rotating rod or bar as the method progresses are relatively cool whereas the rotating rod or bar becomes softened by heating, so that the workpiece is little affected and material from the rod or bar deposits on the workpiece. Lateral movement--i.e. movement of the rod or bar along the surface of the workpiece in a plane at right angles to the plane in which the rod or bar is brought into contact with the surface--is made at a speed that prevents the build-up of sufficient heat at the interface where the rotating rod or bar butts against the workpiece to soften the workpiece, and accordingly the material of the rotating rod or bar deposits on the workpiece.
Experiments have been reported on the phenomena that occur when a rotating rod or bar is brought into contact with a workpiece in the absence of lateral movement--see Fukakusa and Satoh "Travelling Phenomena of Rotational Plane during Friction Welding", Research Reports of Fukui Technical College Natural Science and Engineering, No. 18 (December 1984). The authors describe how the rotational plane or rubbing surface which is the butted plane of the two specimens travels to the inside of one specimen during a frictional heating process and the distance between the travelling rotational plane and the metal boundary plane (the original butted plane) increases with time until it approaches a saturated value. The specimen into which the plane travels is the one in which there is lower resistance to plastic deformation. The reason why the plane is believed to travel is that there is an initial asymmetrical flow of heat across it so that the plane travels until an equilibrium state is reached in which the flow of heat in each direction balances. Experiments are described with combinations of firstly dissimilar material specimens of the same diameter, secondly similar material specimens with different diameters and thirdly dissimilar material specimens with different diameters.
A problem that is not solved by the teaching of the Fukakusa reference is the deposition without lateral movement of a relatively hard material on a relatively soft workpiece, particularly where the workpiece and the rod tube or bar of hard material are of substantially the same diameter.